Building over a sewer/drain

tellisg

Hi,

It looks like the semi-detached house I am purchasing has a drain running at the rear where I propose to build an extension. The property itself has no manholes or visible sewer but I can see that the two adjoining properties have manholes and I assume that a lateral foul drain runs between them in a straight line across my rear garden and close to where my extension foundation would be. The drain runs in a slightly slanted line compared to my extension wall and they cross-over at one point.

Given that a few feet of my rear extension wall will go over the pipe, what options do I have? I have heard about "reinforced concrete floor slab", "cantilever" and "pad foundations and beams" but have no idea what there are and how much more than a standard foundation they would cost.

As I have not exchanged yet, I have no idea of the details of the drain - how big, how deep etc? Also is moving the drain a cheaper option if possible?

The sewage is managed by Thames Water and I have written to them asking for details.

Is my extension a non-starter???

Any advice will be greatly appreciated..... especially as I am exchanging in two weeks

Regards,
T George

missindecisive

you can build over a soil pipe no problem. when you dig your footings for the exstension, if the new walls will go over the pipe you just re-enforce around the pipe with a concrete 'bridge' and then carry on. cant remember how much they cost but not a lot from the builders merchants. we even put our slab floor on top of drains, and the manhole cover is in the garden, it doesn't matter though that yours is in your neighbours garden, so long as there is a rodding point that you can get to. Building control will advise you.

foomanchu

You need to establish who is responsible for the sewer andwhere it is – the normal searches should reveal this. If it is a public sewer runningthough your boundary & is used by neighbours you might not get permissionto build over or move it. While it isn’t common to have a public sewer goingthough your property it does happen, our extension to a 1920s house had to belimited for this reason.

Tucker

I built over mine and moved the inspection access so it was outside the build.

Needs building control to approve the work but it's not usually a show stopper.

mrschaucer

Do remember that since autumn last year water companies have taken over responsibility for repairs etc to joint sewers and lateral drains and I believe the rules have changed as a result of this. I heard somewhere that you now have to get the permission of your water company to build over such pipes and at least some of them will charge for the privilege. They will almost certainly want to ensure that your new extension will not adversely impact "their" drains, so it's not just the buildings control people that you will need to satisfy.

gazza0210

I have just applied to Thames Water for a "buildover agreement" for my rear single storey extension. The agreement costs £343. Building control will not entertain the extension if the buildover isn't in place or applied for. It's all to do with the extensions location to the drain (within 3m and the buildover is needed).

My structural engineer has gone with a "pad & beam" foundation system which floats the exterior wall over the pipes rather than along side.

All the paperwork is in to Thames Water, once I get the answering will either amend as required or if the agreement is in place I will be down to the Waltham Forest planning office, fees in hand for a building notice (hopefully) lol.

If I can help give me a shout.

Good luck my friend.

missindecisive

must depend on your building control officer then! ours didn't bother....there was no mention of contacting water companies with our build. :rotfl:

Tucker

I finished mine 2 and a half years ago, so sounds like I was lucky as it would now be an extra expense!!

SailorSam

When we built our garage there was a drain underneath, a neighbour who had lived there since the house was built just after the War pointed out where the manwhole was in the middle of the garden (it had just been turfed over).
When we built the garage we cut into the sewer and built an additional manhole which the inspector said was Ok to just cover with a marked flag, now another neighbour has built next to us and the regulations changed so it needs fully enclosing, but maybe all boroughs are different.